Addressing smart meter communications challenges
Let’s identify the communications challenges of smart meters and understand how current generations address them today. We will then consider how they should be addressed in order to offer practical and cost-effective and future proof smart grid solutions.
The diagram below shows examples of smart grid network architectures and will help understand why flexibility and multi-mode are key attributes of any new generation smart meter deployment.
Flexibility and multi-mode: key attributes of new generation smart meter deployment
Solutions are diverse and based on numerous technologies depending on geographies, local standards and quality of network infrastructure. The HAN (Home Area Network) or BAN (Building Area Network) uses short range wireless standards such as ZigBee, Thread, WiFi and Bluetooth to connect home appliances to smart meters. It may also use PLC (Power Line Carrier) wireline technology.
The NAN (Neighborhood Area Network) uses either a star network topology such as cellular M2M (GPRS, 3G, LTE MTC, NB-IoT, LPWAN) to connect each meter directly to the base-station and the cloud or a mesh network topology such as PLC or 802.15.4g to aggregate all smart meter nodes to a DAP (Data Aggregation Point) that will be connected directly to the base-station with cellular M2M (GPRS, 3G, LTE MTC) or directly to the cloud via Ethernet.
Flexibility is a must to support all the standards listed above, some of which are still under development and will require updates and remote upgrades in the field. PLC for example, has been standardized by multiple standardization bodies such as IEEE P1901.2, PRIME (PoweRline Intelligent Metering Evolution) and G3 all of which offer multiple variants for data rates and frequency bandwidth.
Countries have also derived variants of PLC to optimize them to the specifics of their electrical power networks. To date there are still no universally agreed interoperability standards governing smart grid communications and there will probably never be one!
Multi-mode is also mandatory as most use-cases require multiple functions to run concurrently. The mesh NAN topology deployed in European and Asian cities calls for concurrent PLC and 802.15.4g as a node may be connected to one node via PLC and to another node via 802.15.4g at the same time.
Extreme low power
While electric smart meters have mains power, non-electric meters must run 5 to 10 years on two AA batteries which requires very careful optimization of both idle and peak power consumption.
Very low cost
To enable fast and widespread deployment of electric smart meters, the complete HAN/NAN communication module bill of material (BOM) should be in the $15 to $20 range.
Existing communication solutions use hardware centric modems which cannot be upgraded to track standards evolution and country variants and cannot support field updates. Therefore Multimode systems are heterogeneous because they consist of a piecemeal collection of independent hardware-based modems. Such heterogeneous solutions are sub-optimal from a power, performance, cost and area standpoint. They also require longer time to market.
Software Defined Modems (SDM) are required to address these challenges with low cost and low power solutions. These modems should run on a unified high performance processor that can run multiple PHYs & Protocols with a true RTOS to support concurrency while minimizing task switching and MAC to PHY latencies.
And at the heart of these flexible communications engines are programmable DSP architectures, such as CEVA-XC5 and CEVA-XC8 that, by supporting a variety of communication standards, allow the developer to implement software-defined modems with no extra hardware requirement. Not only do such architectures reduce time to market but they also minimize risk by offering future-proof solutions that can evolve over the product lifetime by upgrading firmware in the field as standards evolve. Software-only country-to-country customizations allow economies of scale which reduce further the system solution BOM.
Next step: "Smarten" and connect other meters
To make these systems even more challenging, the diagram above shows only a third of the worldwide smart meters, namely the electric meters. Indeed, today, the Smart Grid has been focusing mostly on smart electric meters but the next step is to "smarten" and connect all other meters which include water meters, hot water meters and gas meters.
Although these other meters only need to transmit a few bytes uplink per day and even less downlink, they are more challenging to interconnect than electric meters because they have no built-in power and therefore need a very low power connection that can last 5-10 years without battery recharge. They may also be located in difficult to reach places such as a basement, underground or under water, where radio access may be a challenge. Therefore the link budget needs to be very high and will dictate which technology to choose. For these reasons, the only technology contenders are Cellular MTC (Cat-M, NB-IoT), LPWAN (such as LoRa, Sigfox, …) and WiFi 802.11ah.
About the author
Emmanuel Gresset is Business Development Director, Wireless at CEVA – www.ceva-dsp.com